Application of magnetic hysteresis loop method to determine prior austenite grain size in plain carbon steels

•Effect of prior austenite (PA) grain size changes on magnetic properties was assessed.•Magnetic hysteresis loop (MHL) method was applied to determine PA grain size.•Relations of parameters extracted from MHL and PA grain size were established.•A function was introduced to get three outputs of MHL and give the PA grain size. The present investigation has been performed to explore the ability of magnetic hysteresis loop technique to detect prior austenite grain size changes due to various austenitizing conditions applied in plain carbon steels. To produce various prior austenite grain sizes, AISI 1045 steel specimens were austenitized at 950, 1000, and 1050 °C for 0.5, 1, and 1.5 h. Optical and scanning electron microscopic observations and X-ray diffraction method were conducted to characterize the microstructural features. It was observed that magnetic parameters extracted from hysteresis loop including maximum flux density, maximum differential permeability, and coercivity are affected by variation in prior austenite grain size. Therefore, these magnetic parameters could be used to estimate the prior austenite grain size. Three different functions introduced to do so, each gets a magnetic parameter and gives the estimated value of prior austenite grain size. To enhance the accuracy, another function which takes all three magnetic properties at the same time, were also introduced. It is suggested that the proposed electromagnetic nondestructive method is a useful and accurate enough tool for characterizing the microstructure and quantitative determination of prior austenite grain size of plain carbon steels.